The bHLHzip-type transcription factor, <i>MaHpa3</i> , regulates conidial rodlet formation and cell surface hydrophobicity in the insect fungal pathogen <i>Metarhizium acridum</i>

Fungal conidial hydrophobicity plays critical roles in spore dispersal, host invasion, and environmental adaptation. However, the regulatory mechanisms underlying this phenomenon remain poorly understood. Here, we identified <i>MaHpa3</i>, an uncharacterized bHLHzip-type transcription factor in the insect pathogenic fungus <i>Metarhizium acridum</i>, and demonstrated its role in regulating conidial hydrophobicity along with other cellular processes. Deletion of <i>MaHpa3</i> resulted in reduced conidial yield, altered pigmentation, impaired stress tolerance, attenuated virulence, and decreased conidial hydrophobicity. Scanning electron microscopy revealed structural defects and surface alterations in Δ<i>MaHpa3</i> mutant conidia, including the reduction of the rodlet layer. Additionally, six hydrophobin encoding genes (<i>MaHyd1-6</i>) were identified in the <i>M. acridum</i> genome, and MaHpa3 was shown to act as a positive regulator of the expression of <i>MaHyd2</i>. Targeted deletion of <i>MaHyd2</i> phenocopied the hydrophobicity defect observed in the Δ<i>MaHpa3</i> mutant. Our findings establish MaHpa3 as a key regulator of conidial surface hydrophobicity and rodlet layer formation in <i>M. acridum</i>.